I thought it might be instructive to share some photos of the transformation of my 70g Amazon Flooded Forest aquarium. I initially set this tank up in March 2011 with Flourite Black (enriched) substrate. This was my first use of an enriched substrate, previously having used fine gravel for 20 years. Photo 1 below shows the tank on March 24, 2011, about 3 weeks after setup with the Flourite substrate; plants and wood was transferred over from the former 90g tank. You will note the decent appearance of especially the larger swords, including a red-leaf Echinodorus that I had for about 2 years prior, in the gravel substrate tank.
Photo 2 shows the same tank on January 4, 2012. I wasn't doing much other than weekly 50% water changes and twice weekly doses of Flourish Comprehensive. The red sword was failing, which surprised me considering the substrate, and all else was as it had been in the gravel substrate tank for 2 years.
Photo 3 was the state by November 28, 2012. It looks better than it was. The larger swords had started to fail, and the pygmy chain sword spread was beginning to weaken. I had already determined to tear the tank down and replace the Flourite with play sand, a decision I had come to back in July 2012, due to the disappointing plant growth and the fact that I could not keep substrate fish in this tank due to the sharpness of the substrate. Two weeks ago I finally tackled the task.
Photo 4 is the tank as of yesterday, not quite two weeks after setup with playsand. I saved the only decent plants from the former setup, so this shows how much they had deterioriated. The 41 fish from the former tank went in on Feb 3, and a shipment of 49 wild fish from South America were introduced last Thursday. A group of 12 Corydoras habrosus now frolick over the sand.
A couple of observations. First, now you know why I do not encourage "enriched" substrates. But second, this shows that tanks can be set up with fish without any "cycling" issues, if the plants are sufficient.